ITQ-13分子筛合成及酸性的DFT理论计算研究

以氢氧化已烷双铵(R(OH)2)和溴化六甲双铵(HMBr2)为模板剂分别合成了ITQ-13、B-ITQ-13、Al-ITQ-13分子筛,采用XRD、SEM-EDX、N2吸附-脱附、FT-IR、MAS NMR等手段对合成的分子筛进行表征,比较了两种模板剂合成的ITQ-13分子筛的性质,以溴化六甲双铵(HMBr2)为模板剂,在碱性加晶种的条件下,反应3~10 d合成出了ITQ-13以及含杂原子B、Al的ITQ-13分子筛,降低了合成的成本.以溴化六甲双铵为模板剂合成的ITQ-13晶貌有块状和球形针状堆积混合晶貌组成,孔道宽,晶粒因堆积形成的介孔居多.量子力学中的密度泛函理论(DFT)计算Ge、B、Al同晶取代Si在ITQ-13分子筛9个不同T位的分布,T5位对于ITQ-13分子筛的特殊骨架结构形成具有重要作用,对于骨架的电荷平衡以及几何约束力都有重要作用.Al原子容易替代的位置是位于九元环和十元环孔口相交处的T6、T7位.     

RUB-13分子筛的合成及其甲醇制烯烃催化性能

采用水热法合成RUB-13分子筛,探讨了有机模板剂(OSDA)、硅源、晶化温度和水硅比等制备条件对RUB-13分子筛晶体结构的影响,考察了RUB-13分子筛在甲醇制烯烃(MTO)反应中的催化性能。结果表明,采用1,2,2,6,6-五甲基哌啶(PMP)为有机模板剂、白炭黑为硅源,在晶化温度为170℃的条件下,选择H2O/Si比为100和80时可分别合成出高纯度的低硅铝比(Si/Al=100)和高硅铝比(Si/Al=200)的RUB-13分子筛晶体,且晶粒呈棒状形貌。H-Al-B-RUB-13(Si/Al=200)分子筛用于催化甲醇制烯烃反应时,在400℃下表现出高的低碳烯烃选择性(C2=-5选择性达97. 8%,丙烯选择性为54. 5%),优于传统的H-SAPO-34和H-ZSM-5分子筛催化剂。     

Al-ITQ-13分子筛的快速合成及表征

通过设计首次提出针对ITQ-13分子筛晶化促进剂的合成策略,ITQ-13分子筛.通过X射线粉末衍射(XRD)、扫描电子显微镜(SEM)、N2吸附、原位红外(FTIR)及固体核磁(27Al NMR)等测试手段对ITQ-13分子筛的物化性能进行了表征,考察了晶化过程中结晶度的变化,得出了晶化过程的动力学参数,对晶化机理进行了探讨.结果表明:快速合成法与传统方法合成的ITQ-13分子筛具有相似的物化性能,并且可以合成含有更多骨架铝的ITQ-13分子筛;NO3-的加入通过极化憎水基团,加速SiOSi物质结合,降低ITQ-13分子筛的成核活化能以及生长活化能,从而可以提高晶化速率,缩短晶化时间至11 h.     

在(TPA)2O-Na2O-SiO2-H2O系统中MFI型硅沸石的结晶行为(Ⅰ)──结晶动力学的研究

以四丙基溴化按作模板剂,以白炭黑(Ⅰ)、硅溶胶(Ⅱ)和水玻璃(Ⅲ)为不同硅源在140～180℃合成MFI型硅佛石(Silicalite－1).反应物配比相同,其结晶动力学曲线有明显差异.从它们的成核诱导期及生长速度计算出各体系硅佛石晶核形成活化能与生长活化能,在体系(Ⅰ)中为46/76kJ/mol,体系(Ⅱ)中为41/43kJ/mol,体系(Ⅲ)中为38/78kJ/mol.产物结晶粒径的大小由各体系成核活化能与生长活化能的差值决定.合成产物的结晶度以白炭黑为硅源时最高.提高温度有利于提高产物结晶度.     

膨胀剂用量、合成体系pH值和MCM-22（P）的硅／铝比对ITQ-2分子筛合成的影响

考察了膨胀剂的用量、合成体系的pH值和MCM-22(P)的硅/铝比对合成ITQ-2分子筛的影响. 结果表明,同时降低膨胀剂十六烷基三甲基溴化铵和四丙基氢氧化铵的用量,在pH=11.5时 4 h 即可完成对MCM-22(P)的插层膨胀;pH值降低时,可减小由于脱硅对ITQ-2分子筛硅/铝比下降的影响,并且使产物收率大幅度提高. 同时, pH值降低使后续的超声剥离更加容易,且可避免生成MCM-41介孔分子筛杂相. MCM-22(P)的硅/铝比越大,层表面的电荷密度越低,带负电荷的层板和阳离子插层剂之间的静电引力和分子间作用力也就越小,致使插层膨胀和随后的超声剥离越容易.     

硅源对MCM-22分子筛合成及物化性质的影响

在动态水热条件下,研究了硅溶胶、白炭黑、硅酸及硅胶为硅源时对MCM-22分子筛合成及物化性质的影响。以硅溶胶、白炭黑、硅酸三种硅源均可合成出高结晶度且无杂晶的片状MCM-22分子筛,其平均粒径分别为190、220和750 nm。硅源影响分子筛的聚集形态,三种硅源分别形成晶粒分散、晶粒半分散及晶粒聚集形态。三组样品的酸强度分布基本一致,都具有较多的中强酸分布,由硅溶胶和硅酸所得MCM-22分子筛在中强酸范围具有更高的B/L酸比值,以白炭黑合成的分子筛总酸量最高。NMR结果表明,样品中的铝以骨架铝为主,不存在明显的非骨架铝。由于硅胶对合成体系中游离水的吸附作用,水热反应难以发生,不能得到MCM-22分子筛,硅胶作为分子筛合成硅源时需要选择合适的反应条件。     

以季磷化合物为模板剂合成超大孔分子筛ITQ-33

以四丁基氢氧化磷为模板剂, 在中温水热条件下, 利用浓溶胶法合成了具有一维18元环孔道的含铝硅锗酸盐分子筛ITQ-33. 系统研究了ITQ-33的合成条件, 并利用原位变温X射线衍射(XRD), 扫描电子显微镜(SEM), 固体核磁共振波谱(NMR), 电感耦合等离子体发射光谱(ICP), 氮气吸附-脱附程序升温脱附(TPD), 热重(TG)及元素分析等手段对其结构、 稳定性及催化性能进行了表征. 结果表明, 以季磷化合物为模板剂可以合成含铝的ITQ-33纯相, 产物具有较高的热稳定性, 其骨架结构可以稳定至400℃以上, 煅烧后的ITQ-33具有Lewis酸位点, 在酸催化方面有潜在的应用价值.     

RUB-13分子筛的合成及其甲醇制烯烃催化性能

采用水热法合成RUB-13分子筛，探讨了有机模板剂（OSDA）、硅源、晶化温度和水硅比等制备条件对RUB-13分子筛晶体结构的影响，考察了RUB-13分子筛在甲醇制烯烃（MTO）反应中的催化性能。结果表明，采用1，2，2，6，6-五甲基哌啶（PMP）为有机模板剂、白炭黑为硅源，在晶化温度为170℃的条件下，选择H₂O/Si比为100和80时可分别合成出高纯度的低硅铝比（Si/Al=100）和高硅铝比（Si/Al=200）的RUB-13分子筛晶体，且晶粒呈棒状形貌。H-Al-B-RUB-13（Si/Al=200）分子筛用于催化甲醇制烯烃反应时，在400℃下表现出高的低碳烯烃选择性（C_2-5⁼选择性达97.8%，丙烯选择性为54.5%），优于传统的H-SAPO-34和H-ZSM-5分子筛催化剂。     

使用四乙基氢氧化铵作为有机模板剂和常规硅铝源直接合成SSZ-13沸石分子筛

使用四乙基氢氧化铵作为有机模板剂, 利用常规铝源和硅源而不需要高硅Y沸石作为起始原料, 同时加入适量的沸石晶种直接合成了SSZ-13沸石分子筛. 所合成的沸石产物结晶度好, 具有良好的水热稳定性, 并在氨选择性催化还原(NH₃-SCR)反应中显示出优异的催化性能, 为其在工业上广泛应用提供了可能.     

乙醇法合成硼硅Pentasil型分子筛

七十年代,美国Mobil公司^[1]发表了ZSM-5型沸石分子筛的专利,该沸石具有独特的结构和良好的催化性能,在石油化工技术中业已展现出广阔的应用前景.1980年,M.Taramasso^[2]等人用四丙基胺、正硅酸乙酯等原料合成出了四种硼硅分子筛.1981年,作者^[3]在国内首次用有机胶合成出硼硅Pentasil型分子筛(ZSM-5型).本文以水玻璃、白炭黑为硅源,用乙醇取代有机胺,在微量导向剂存在下,合成了硼硅pentasil型分子筛;并用正交实验的方法探讨了合成中诸因素对分子筛结晶度的影响.     

Effect of silicon precursor on silicon incorporation in SAPO-11 and their catalytic performance for hydroisomerization of n-octane on Pt-based catalysts

SAPO-11 molecular sieves were synthesized using silica sol, hydrophilic fumed silica, and tetraethyl orthosilicate(TEOS) as silicon precursors. Their physicochemical properties were characterized using XRD,SEM, nitrogen adsorption-desorption, Py-IR, NH_3-TPD, EDS, and ~(27)Al,~(31)P,~(29)Si MAS NMR techniques. The catalytic performance was assessed in the hydroisomerization of n-octane. The results showed that the silicon precursors influenced the physicochemical properties and catalytic performance of SAPO-11. SAPO-11 synthesized using hydrophilic fumed silica as silicon precursor showed higher silicon distribution and had more medium acid sites. SAPO-11 synthesized using TEOS as silicon precursor had more silicon content, but more silicon islands formed in its framework. The depolymerization of silicon precursors might affect the silicon content and distribution in SAPO-11. In the hydroisomerization of n-octane, the catalytic activity strongly depended on the number of medium acid sites instead of the number of total acid sites.SAPO-11 synthesized using hydrophilic fumed silica as silicon precursor exhibited higher catalytic activity than the other samples because it has more medium acid sites.     

Synthesis and crystal structure of As-synthesized and calcined pure silica zeolite ITQ-12

The small-pore pure silica zeolite ITQ-12 has been synthesized with fumed silica as the silica source in the presence of 1,3,4-trimethylimidazolium hydroxide and hydrofluoric acid under hydrothermal conditions at 448 K. Rietveld refinement using synchrotron X-ray diffraction data of the calcined ITQ-12 product taken at 298 K confirms the proposed topology, framework type code ITW, which can be described by a monoclinic unit cell [Si(24)O(48)] having Cm symmetry. Unit cell parameters are a = 10.3360(4), b = 15.0177(6), and c = 8.8639(4) A, beta = 105.356(3) degrees, and cell volume V = 1326.76(9) A(3). For as-synthesized ITQ-12, the occluded fluoride anion is located inside the double four-membered ring, while the flat 1,3,4-trimethylimidazolium cation lies on the equatorial plane of the slit-shaped [4(4)5(4)6(4)8(4)] cage, with its longest dimension in the [010] direction. The monoclinic unit cell |(C(6)N(2)H(11))(+)(2)F(-)(2)|[Si(24)O(48)], having Cm symmetry, has parameters a = 10.4478(3), b = 14.9854(4), and c = 8.8366(3) A, beta = 105.935(2) degrees, and cell volume V = 1330.34(7) A(3) at 298 K. Cooperative structure-directing effects during the crystallization of ITQ-12 are discussed in terms of the structure of the as-made material.     

COMPARISON BETWEEN TETRAETHYL ORTHOSILICATE AND AMORPHOUS SILICA AS SILICA SOURCES FOR SYNTHESIZING ZEOLITE ZSM-35

IntroductionZeoliteZSM-35,becauseofitssatisfactorycarelyticpropertiesandcompafativelyhighSiOZ/A12O3ratio,hasattractedconsiderableeffortsleadingtofindtheappropriatesyntheticconditionsforopticalcharactCristicsofproducts.Inadditiontoconventionalhydrothermals…     

Effect of solvent type on polycondensation of TEOS catalyzed by DBTL as used for stone consolidation

We have investigated the effect of solvent in the sol–gel process of tetraethylorthosilicate (TEOS) when di-n-butyltin dilaurate (DBTL) is used as polycondensation catalyst. Two sets of materials similar to those employed in the field of stone consolidation were prepared in the laboratory by using either protic or aprotic solvents: (1) xerogels from TEOS/DBTL, and (2) composites from TEOS/colloidal silica particles/DBTL. The results have shown that the solvent directly influences the aggregation pathway of the condensates. For a mixture of methyl ethyl ketone/acetone (aprotic solvents), gels with a higher degree of condensation were obtained. In the case of TEOS xerogels, the materials are essentially non-porous. Additionally, the incorporation of colloidal silica particles induces an important increase in porosity, which is even more dramatic when ethanol is used as solvent, through the formation of micro and mesoporous materials as the concentration of particles is increased. A TEOS polymerization pathway is suggested depending on which system of solvents is used. Various analytical techniques were used to characterize the materials obtained.     

纳米二氧化硅的表面改性研究

以γ-缩水甘油醚丙基三甲氧基硅烷(GPTMS)对酸催化水解正硅酸乙酯(TEOS)聚合得到的纳米二氧化硅胶粒表面进行接枝改性,用激光粒径仪测定二氧化硅颗粒的粒径,并用透射电子显微镜(TEM)观察了改性前后二氧化硅胶粒的分散状况,采用傅立叶红外(FTIR)光谱法对改性前后的二氧化硅粉体进行了分析,通过热失重分析(TGA)法对GPTMS接枝改性二氧化硅胶粒表面的接枝度进行分析计算,同时对颗粒溶胶的ζ电位进行了测试,结果表明:改性后二氧化硅胶粒分散性大大提高,硅烷偶联剂浓度对接枝度有显著影响,当GPTMS的浓度为1mL/S iO2(g)时,接枝度达到最大,且颗粒表面的物理化学性能发生显著变化。     

Tailored core-shell-shell nanostructures: sandwiching gold nanoparticles between silica cores and tunable silica shells

Size tunable and structure tailored core-shell-shell nanospheres containing silica cores, gold nanoparticle shells, and controlled thicknesses of smooth, corrugated, or porous silica shells over the gold nanoparticles have been synthesized. The synthesis involved the deposition of gold nanoparticles on silica cores, followed by sol-gel processing of tetraethoxysilane (TEOS) or sodium silicate to form dense or porous silica shells, respectively, over the gold nanoparticles. The structures and sizes of the resulting core-shell-shell nanospheres were found to heavily depend on the sizes of the core nanoparticles, the relative population of the gold nanoparticles on each core, and the concentration of TEOS. While a higher TEOS concentration resulted in thicker and more uniform silica shells around individual larger silica cores (approximately > or =250 nm in diameter), the same TEOS concentration resulted in aggregated and twin core-shell-shell nanostructures for smaller silica cores (approximately < or =110 nm in diameter). The thinner silica shells were synthesized by using a lower TEOS concentration. By using sodium silicate (Ung et al. J. Phys. Chem. B 1999, 103, 6770), the porous silica shells were synthesized. Controlled chemical etching of the core-shell-shell nanoparticles with an aqueous KCN solution resulted in corrugated silica shells around the gold nanoparticles or corrugated silica nanospheres with few or no gold nanoparticles. This has allowed synthesis of new types of core-shell-shell nanoparticles with tailored corrugated shells. The nanoporous silica shells provided accessible structures to the embedded metal nanoparticles as observed from the electrochemical response of the gold nanoparticles.     

Preparation of nearly monodisperse multiply coated submicrospheres with a high refractive index

Nearly monodisperse SiO2/TiO2/SiO2 multiply coated submicrospheres with nearly monodisperse silica submicrospheres as cores, thick titania layers, and thin silica skin were prepared to increase the refractive index of complex submicrospheres while keeping their near monodispersity and perfect surface properties. Nearly monodisperse colloidal silica submicrospheres as cores with a diameter of 200 nm were synthesized by a seeding technique on the basis of the hydrolysis of tetraethyl orthosilicate (TEOS) in an aqueous ethanol solution with ammonia as catalyst. On the basis of the hydrolysis of tetrabutyl orthotitanate, a procedure combining continuous feeding with multistep coating was determined to prepare titania coatings about 40 nm thick and increase the refractive index of the complex submicrospheres. The hydrolysis of TEOS was still used to get the outmost silica coating about 10 nm thick on titania coated silica submicrospheres to eliminate random aggregation caused by the TiO2 surface properties of the TiO2/SiO2 complex submicrospheres during the final fabrication of photonic crystals.     

Development of various PS-b-P4VP micellar morphologies: fabrication of inorganic nanostructures from micellar templates

A liquid-phase method for preparing uniform-sized silica nanospheres (SNSs) 12 nm in size and their three-dimensionally ordered arrangement upon solvent evaporation have recently been pioneered by us. Here we report the successful control of the sphere sizes in the wide range from 14 to 550 nm by the seed regrowth method. In this method, the dispersion of SNSs 14 nm in size as seeds was prepared in the emulsion system containing Si(OEt)(4) (TEOS), water and arginine under weakly basic conditions (pH 9-10). An appropriate portion of this dispersion is added to the solution containing water, ethanol and arginine, and then TEOS is added. The additional TEOS introduced into the regrowth system contributed only to the resumed growth of the seeds, not to the formation of new silica particles. The size of interparticle pores was finely tuned by changing the size of the spheres. The preparation of three-dimensionally ordered porous carbons by using the colloidal array of silica nanospheres as a template is also reported.     

核壳型复合分子筛ZSM-5/Nano-β的合成与表征

以ZSM-5小晶粒为核相材料, 用聚二烯丙基二甲基氯化铵(PDDA)进行表面预处理后, 黏附nano-β晶种并焙烧制得核相晶种, 再在壳层晶化生长体系中通过水热合成得到ZSM-5/nano-β有序的核壳分子筛. 产物的物相和结构通过XRD, SEM, TEM以及N₂吸附/脱附分析表征, 通过对比发现, β壳层的合成以白炭黑为硅源比用正硅酸乙酯(TEOS)更好. 通过NH₃-TPD表征, 以及1,3,5-三甲苯裂化转化反应对分子筛的性能进行了考察, 结果表明, 核壳分子筛通过调变组成分子筛的酸性, 从而大大提高了材料的催化裂化性能, 同时延缓了失活速率.